SPID#: 36 While the endocrine and physiological parameters of the human menstrual cycle are well documented, precise details of the 'fertile' (as identified by established pregnancy) as opposed to the 'nonfertile' cycle, are not well defined. In addition, there is a recognized incidence of 'idiopathicinfertility' which exists even when male factors have been eliminated. Such rnormals though rinfertiles cycles also appear to occur in female common chimpanzees (Pan troglodytes), and have been identified by detailed monitoring of estrogen and progesterone fluctuations. It is hypothesized that the infertility is due to altered protein expression by the endometrium at time of implantation; this alteration appears to follow on from a distinctive pattern of estrogen secretion during the follicular phase. A matched series of serum samples and endometrial biopsies were collected from the two types of cycle using a sensitive external marker of follicular activity (the Perineal Swelling pattern) to distinguish the two types of cycle and schedule the sampling. Serum samples were obtained between six and nine days after menses either before or after a critical change in the marker; this change has been demonstrated to occur immediately prior to a doubling of estrogen concentrations. Endometrial biopsies were collected during the luteal phase five days after the peri-ovulatory peak in luteinizing hormone (LH) and three or four days after a distinctive and associated alteration in the external marker. These biopsies are being processed to identify the relative expression of various integrins (attachment proteins), particularly (V(3, which has been shown to vary in expression during the luteal phase. Histological sections are subject to quantitative fluorescence microscopy. After quantitation of the protein expression, we will verify the predicted fertility status of the cycle by use of artificial insemination, a technique which can now achieve greater than 80% pregnancy after a single insemination.